Agricultural machines, such as a combine, include different portions or sections for moving crop therethrough. For example, a conventional combine may include a cleaning shoe or system that is located between the wheels of the combine, behind the cab and below the engine. The design of the cleaning system is such that a large fan or blower provides air driven upward therefrom. The cleaning system may include grating in the form of a large cylindrical or semi-circular body through which grain and other residue falls through and onto a cleaning shoe (or sieve). Air from the blower is generated upward through the flat grating and cleaning shoe and lifts material other than grain (“MOG”) such as straw and carries the material to the rear of the combine on a flow of air. Grain that falls through a large flat screen of the cleaning system may collect near a bottom of the combine where it is lifted up by the air flow and deposited into a grain tank. The MOG is further carried by the air flow over the top of the sieve and to the rear of the combine where it is deposited onto the underlying ground. In effect, this performs the cleaning function of the combine. The MOG, which is carried by the air flow to the rear of the combine, may be spread on the ground or otherwise deposited on the ground in a narrow windrow or swath where it is later picked up.
The combine further includes a straw chopper or chopper assembly located between the sieve and the rear outlet of the combine. The chopper assembly may be formed by a large cylinder with blades or knives protruding therefrom, thereby forming a chopper rotor. The chopper assembly rotates and shreds or chops the residue or MOG before it exits the combine.
During operation, the blower generates a substantial amount of air flow to carry the MOG to the chopper assembly. The amount of air generated by the blower is significant, and in effect it can cause back pressure inside the combine if it is unable to escape or vent from the enclosed combine body. Conventional combine designs include vents upstream of the chopper assembly to allow air to vent or escape from the combine to reduce back pressure.
One such example of venting air is described in U.S. Pat. No. 7,008,315 to Redekop Chaff Systems Ltd. (hereinafter “the '315 patent”). The '315 patent describes a chopper housing formed by side walls at opposite sides of a combine hood. The housing further includes a top wall and a bottom wall that define an inlet which straw and other material passes through to a chopper rotor. As shown in FIG. 2 of the '315 patent, the top wall of the housing includes a vertical portion which extends downwardly and a curved section that extends around the top of the rotor to a rear edge which is directly to the rear of the rotor. In other words, the '315 patent shows and describes a shroud or metal sheet which is formed around or circumscribes all sides, including the rear or back side, of the chopper rotor. Due to a buildup of back pressure in the combine, the '315 patent further illustrates and describes a combine with rear vents and side vents defined in the chopper housing. The vents form a series of horizontal parallel slots and consist of louvers that are angled outwards and upwards. Moreover, the vents are above and forward of the inlet of the chopper housing so as to act on the air in advance of the materials entering the inlet of the chopper rotor. Thus, the '315 patent describes a combine in which air is permitted to vent or escape from the combine at a location above and upstream of the chopper rotor.
In addition to the rear vents and side vents, the '315 patent further describes the chopper rotor as including a hub with a plurality of radially extending blades which rotate and are arranged across the width of the chopper rotor. The blades are configured to generate an air flow by pushing the air rearward toward an outlet of the rotor housing. During operation, the blades rotate about the hub and push the air to follow a generally circular path around the chopper rotor.
Combine harvester designs similar to the one described in the '315 patent, however, have been found to restrictive to air flow. The vents upstream of the chopper rotor facilitate some venting, but there is still an issue with back pressure building in the combine even with these vents. Moreover, air flow is further restricted with chopper rotor housings similar to the one in the '315 patent in which sheet metal or a shroud is formed in close proximity around the top and rear of the chopper rotor. Due to the close proximity of the shroud to the blades of the chopper rotor, the air flow is configured to follow the rotational path of the blades. Although the blades, which may be formed like paddles or fan blades, facilitate some air flow through an outlet of the chopper housing, the air flow is still restricted by the design of the chopper housing and the fan blades cause some of the air to flow forward back into the combine thus building back pressure. Thus, there is a need for a less restrictive chopper housing design that facilitates better air flow through an outlet of the chopper housing and which reduces back pressure in the combine.